1. Field of the Invention
One or more embodiments of the present invention relate to a composite anode active material, a method of preparing the composite anode active material, and an anode and lithium battery including the composite anode active material.
2. Description of the Related Art
Carbonaceous materials such as graphite are representative examples of anode active materials for lithium batteries. Graphite has excellent capacity retention characteristics and excellent voltage characteristics. In addition, graphite does not vary in volume when it is used to form an alloy with lithium. Therefore, anode including graphite may increase the stability of a battery. Graphite has a theoretical electrical capacity of about 372 mAh/g and a high irreversible capacity.
In addition, metals capable of forming alloys with lithium may be used as an anode active material for lithium batteries that has a higher electrical capacity than that of carbonaceous materials. Examples of metals capable of forming alloys with lithium include silicon (Si), tin (Sn), aluminum (Al), and the like. These metals have a very high electrical capacity. For example, a theoretical storage capacity of Si is 4,200 mAh/g. Such metals undergo volumetric expansion during charging and discharging of the batteries, thereby electrically isolating the active material within the electrode. In addition, an electrolyte decomposition reaction becomes severe, due to an increase in specific surface area of the active material. Moreover, a lithium battery including metals capable of forming alloys with lithium exhibits reduced capacity retention characteristics. For example, when the batteries are repeatedly charged and discharged, Si particles in the anode active material repeatedly aggregate with each other and are repeatedly crushed; therefore, Si is electrically disconnected from a current collector. Furthermore, metals capable of forming alloys with lithium are thermally unstable and thus problems such as thermal runaway may occur.
Therefore, there is a need to develop a method of manufacturing a lithium battery that includes a metal capable of forming alloys with lithium and has high capacity, excellent lifetime characteristics, and high thermal stability.